There has been a continuing need for high temperature resistant radiation resistant insulated wire products. One of the best materials for this type of application is polyimide polymer insulation which has the chemical composition to withstand both high temperature and radiation better than most polymeric materials. Typical useful materials are polyimides disclosed and claimed in U.S. Pat. No. 3,129,634 wherein organic aromatic tetravalent acids react with at least one organic divalent benzenoid diamine to give preferably an all aromatic ring structured polyamide-acid intermediate. These intermediates can be made into films or solutions which, after the solvent is removed, can be cured by heating above 50.degree. C. to the fully aromatic polyimide. The polyamide-acid in the form of wire enamel is made by fully curing by baking the polyamide-acids and similar abrasion-resistant baked wire coatings on other insulation and layered with fluorocarbon adhesives as tape wrap wire insulation.
Two problems exist, however, which limit the use of the material in these forms. First, the dielectric constant of the films is high (3.5) as compared to expanded, stretched, or foamed alternative materials (1.3-2.2). Second, where a fluorocarbon thermoplastic adhesive is used in combination with polyimide tape or film, such as disclosed in U.S. Pat. Nos. 3,168,417, 3,352,714 and 3,40B,715, the fluorocarbon is not radiation resistant, and the advantage of radiation resistance is nullified for these tapes. Alternative adhesives which could be substituted, such as polyester, polyurethane, or acrylic, are limited in temperature resistance, however, so that solution is not fully satisfactory.